The goal of this research is to determine the nature of the electronic response of large molecule systems, especially biological helical polymers, to strong perturbations such as is provided by laser excitation. One purpose is to determine conditions for effective resonances to be operative in systems having many degrees of freedom. Three specific areas are as follows: (1) The nucleic acid bases are being studied in terms of linear response theory, in which the Time Dependent Hartree (TDH) level of approximation is used to obtain the density response function for pi-electrons. This enables the calculation of absorption spectra (including polarizations) and atom-centered transition densities. (2) The linear response tensor in the TDH approximation is developed for helical polymers in a manner which fully utilizes symmetry and exciton selection rules in order to provide simple, closed-form expressions for circular dichroism spectra. The theory naturally emphasizes the role of molecular geometry. (3) Experimental studies will be conducted on the selective excitation of large molecules with continuous dye lasers. The objective is to determine the nature of the resonances excited by nonlinear driving of dense spectra.